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1
Reddy, Yeruva S. "Numerical simulation of damage and progressive failures in composite laminates using the layerwise plate theory". Diss., Virginia Tech, 1992. http://hdl.handle.net/10919/38534.
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Akileh, Aiman R. "Elastic-plastic analysis of axisymmetrically loaded isotropic circular and annular plates undergoing large deflections". PDXScholar, 1986. https://pdxscholar.library.pdx.edu/open_access_etds/3559.
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The concept of load analogy is used in the elastic and elastic-plastic analysis of isotropic circular and annular plates undergoing moderately large deflection. The effects of the nonlinear terms of lateral displacement and the plastic strains are considered as additional fictitious lateral loads, edge moments, and in-plane forces acting on the plate. The solution of an elastic or elastic-plastic Von Karman type plate is hence reduced to a set of two equivalent elastic plate problems with small displacements, namely, a plane problem in elasticity and a linear elastic plate bending problem. The method of finite element is employed to solve the plane stress problem. The large deflection solutions are then obtained by utilizing the solutions of the linear bending problems through an iterative numerical scheme. The flow theory of plasticity incorporating a Von Mises layer yield criterion and the Prandtl-Reuss associated flow rule for strain hardening materials is employed in this approach.
3
Banan, Roshan Aerospace Civil & Mechanical Engineering Australian Defence Force Academy UNSW. "An engineering approach to modelling ballistic impact on hybrid polymer laminates". Publisher:University of New South Wales - Australian Defence Force Academy. Information Technology & Electrical Engineering, 2009. http://handle.unsw.edu.au/1959.4/44094.
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Hybrid polymer laminates of polycarbonate and PMMA have generated considerable interest among researchers as an alternative to traditional glass armours because of their potential for reduced cost and weight. Generally, the development of ballistic armour is carried out experimentally which is an expensive task in terms of time and cost. Numerical simulation provides a much greater facility to understand the phenomenon of ballistic impact and the effects of various parameters on the response to such impact. In addition it provides an easy means of comparing the impact performance of different materials as well as combination of materials forming hybrid laminates. The aim of this research was to develop a numerical modelling capability to simulate the ballistic response of hybrid polymer laminates, specifically polycarbonate and PMMA, using a commercially available finite element code LS-DYNA. The challenge was to work within the limitations of the material models and the failure algorithms available within LS-DYNA, and still try to reproduce the behaviour observed experimentally by previous researchers, initially on monolithic plates of polycarbonate and PMMA and then on hybrid laminates. The first part of the study focuses on a detailed literature survey on mechanical and dynamic characterisation of polycarbonate and PMMA as well as experimental and numerical studies previously conducted on ballistic behaviour of these materials as well as their combinations. The material properties of the polymers compiled from this literature survey were used as input for the selected LS-DYNA material model. Impact simulations were carried on monolithic and laminated media of polycarbonate and PMMA and where possible these were compared to experimental results. It was observed that the results agreed with the experimental data qualitatively. Quantitatively the results showed some discrepancies which were attributed to the limitations faced in simulating the exact test conditions numerically. Numerical simulations were carried out to study the effects of variations in laminate thickness and plate support diameters as well as to examine the influence of the bond between the layers. Finally the impact response of four different combinations of polycarbonate and PMMA are compared to each other for different laminate thicknesses.
4
Young, Andrew J. "Active control of vibration in stiffened structures". Title page, contents and abstract only, 1995. http://hdl.handle.net/2440/37722.
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Active control of vibration in structures has been investigated by an increasing number of researchers in recent years. There has been a great deal of theoretical work and some experiment examining the use of point forces for vibration control, and more recently, the use of thin piezoelectric crystals laminated to the surfaces of structures. However, control by point forces is impractical, requiring large reaction masses, and the forces generated by laminated piezoelectric crystals are not sufficient to control vibration in large and heavy structures. The control of flexural vibrations in stiffened structures using piezoceramic stack actuators placed between stiffener flanges and the structure is examined theoretically and experimentally in this thesis. Used in this way, piezoceramic actuators are capable of developing much higher forces than laminated piezoelectric crystals, and no reaction mass is required. This thesis aims to show the feasibility of active vibration control using piezoceramic actuators and angle stiffeners in a variety of fundamental structures. The work is divided into three parts. In the first, the simple case of a single actuator used to control vibration in a beam is examined. In the second, vibration in stiffened plates is controlled using multiple actuators, and in the third, the control of vibration in a ring-stiffened cylinder is investigated. In each section, the classical equations of motion are used to develop theoretical models describing the vibration of the structures with and without active vibration control. The effects of the angle stiffener(s) are included in the analysis. The models are used to establish the quantitative effects of variation in frequency, the location of control source(s) and the location of the error sensor(s) on the achievable attenuation and the control forces required for optimal control. Comparison is also made between the results for the cases with multiple control sources driven by the same signal and with multiple independently driven control sources. Both finite and semi-finite structures are examined to enable comparison between the results for travelling waves and standing waves in each of the three structure types. This thesis attempts to provide physical explanations for all the observed variations in achievable attenuation and control force(s) with varied frequency, control source location and error sensor location. The analysis of the simpler cases aids in interpreting the results for the more complicated cases. Experimental results are given to demonstrate the accuracy of the theoretical models in each section. Trials are performed on a stiffened beam with a single control source and a single error sensor, a stiffened plate with three control sources and a line of error sensors and a ring-stiffened cylinder with six control sources and a ring of error sensors. The experimental results are compared with theory for each structure for the two cases with and without active vibration control.Thesis (Ph.D.)--Mechanical Engineering, 1995.
5
Liu, Bing 1975. "FE analysis of plastic buckling of plates with initial imperfections and simulation of experiments". Thesis, McGill University, 2007. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=100251.
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The general problem of plastic buckling of flat metal plates is a fundamental area of investigation in mechanics not only because of its intrinsic importance in the design of engineering structures, but also because it still has not been settled in a satisfying manner. Which theory of plasticity is the correct one to predict the buckling loads in the plastic range is a long-argued problem.This thesis presents finite element analyses of plastic buckling and postbuckling behaviour of columns and plates, taking into account the presence of initial out-of-plane imperfections. The FE programs constructed by the author for this purpose are used to analyze the imperfection growth of such columns and plates under axial loading and simply supported edge conditions. The material behaviour is modeled according to both the incremental and the deformation theories of strain-hardening plasticity. The programs combine both the geometric and material nonlinearities to trace the load-deflection behaviours of these structures in prebuckling (up to the maximum load) as well as postbuckling ranges. The results of the analyses for plates show the extreme sensitivity of the incremental theory, and the relative insensitivity of the deformation theory, to the initial imperfections.
The programs are used to simulate the plastic buckling experiments on Aluminum tubes, taking into account their measured imperfections. The imperfection growth analyses demonstrate that the maximum load predictions of the incremental theory are quite close to those recorded in the experiments.
6
Robbins, Donald H. "Hierarchical modeling of laminated composite plates using variable kinematic finite elements and mesh superposition". Diss., Virginia Tech, 1993. http://hdl.handle.net/10919/40117.
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CHAKRABARTI, SEKHAR KUMAR. "INELASTIC BUCKLING OF GUSSET PLATES". Diss., The University of Arizona, 1987. http://hdl.handle.net/10150/184188.
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The strength and behavior of gusset plates in buckling is evaluated herein based on data from the experimental investigations conducted by other researchers and the analytical work presented herein. A set of design guidelines has been recommended through the review of the current practice. Representative single and double brace gusset plates normally adopted for connections with compressive bracing/diagonal members in braced frames and trusses, were modeled and analyzed using linear and nonlinear finite element methods to determine the buckling loads. The buckling analysis data along with the test data indicated the occurrence of inelastic buckling of the gusset plates. Current design practice and a set of formulas for determination of gusset plate thickness have been reviewed. A set of guidelines has been recommended for the design and evaluating gusset plate buckling loads.
8
Abel, Mary Sue M. "Four-bolt extended unstiffened moment end-plate connections". Thesis, This resource online, 1993. http://scholar.lib.vt.edu/theses/available/etd-11242009-020221/.
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Montgomery, Darcy Thomas. "Milling of flexible structures". Thesis, University of British Columbia, 1990. http://hdl.handle.net/2429/29689.
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Current manufacturing research aims at increasing productivity by optimal selection of process parameters. This is accomplished by understanding the fundamental physics of individual manufacturing processes.
In this thesis, peripheral milling of very flexible cantilevered plates is studied. The static and dynamic deflections of the plate under periodic milling forces are modelled. A new dynamic cutting force model is developed which considers five discrete zones of relative motion between the tool and the workpiece. The kinematics of both milling and vibratory motions are modelled, which is an original research contribution in this area. It is shown that the penetration of the tool into the workpiece during vibratory cutting has a strong influence on the damping and stiffness characteristics of the milling process.
A structural model of a discontinuous cantilevered plate is determined using the finite element method. A reduced order structural model at the tool-workpiece contact zone is implemented for discrete time response analysis of the plate under cutting force excitations during milling. The closed loop dynamic behaviour of the system is modelled and taken into account in the analysis. Simulations of plate machining are compared with experimental results. A model of the surface finish generation mechanism is deduced from the analysis and experimental results.
Applications of this research include peripheral milling of integral jet engine impellers, computer disk drives and other flexible mechanical components.Applied Science, Faculty of
Mechanical Engineering, Department of
Graduate
10
張啓軍 e Qijun Zhang. "The Galerkin Element Method and power flow in acoustic-structural problems with damped sandwich plates". Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 1999. http://hub.hku.hk/bib/B31239742.
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Wong, Man-kie, e 黃文基. "A study of capacity predictions for driven piles by dynamic pile testing". Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2006. http://hub.hku.hk/bib/B37106120.
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王偉洪 e Wai-hung Wong. "A study of constitutive models on engineering properties of Hong Kong marine clay". Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 1997. http://hub.hku.hk/bib/B31214745.
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Nugroho, Widijanto Satyo. "Waves generated by a load moving on an ice sheet over water". Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1997. http://www.collectionscanada.ca/obj/s4/f2/dsk2/ftp03/NQ32720.pdf.
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Yu, Wenbin. "Variational asymptotic modeling of composite dimensionally reducible structures". Diss., Georgia Institute of Technology, 2002. http://hdl.handle.net/1853/12225.
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Skeen, Michael Berling Mechanical & Manufacturing Engineering Faculty of Engineering UNSW. "An investigation of energy flow through coupled plate structures". Publisher:University of New South Wales. Mechanical & Manufacturing Engineering, 2008. http://handle.unsw.edu.au/1959.4/43277.
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This PhD thesis presents research aims to improving the dynamic modelling of coupled plate structures across a wide frequency range by using analytical, statistical and experimental methods. The analytical waveguide method is used to model the flexural displacement of coupled plate structures which are simply supported along two parallel edges. A method of quickly predicting the average energy level in a plate from details of the waveguide model is described, and used for comparison with SEA models. The Poynting and Impedance methods of predicting the energy flow in coupled plate structures are investigated. Transmission coefficients for coupled plate structures are evaluated using the analytical waveguide method for both semi-infinite and finite coupled plate structures. Finite transmission coefficients have traditionally been more difficult to evaluate due to the presence of a reverberant field, but in this work a novel method of separating the reverberant field using a scattering matrix method is presented. The transmission coefficients for semi-infinite and finite structures are then compared for L-shaped plates. A modal transmission coefficient is also defined and for the cases considered, and is used to develop an alternative method of deriving the transmission coefficient in a finite structure. Frequency averaged transmission coefficients are also considered, and the transmission coefficients derived for finite and semi-infinite structures are found to be very similar after frequency averaging. Statistical Energy Analysis models of coupled plates are evaluated using transmission coefficients derived from waveguide models. The results of the SEA models are compared to those predicted by the analytical waveguide method. A modal transmission coefficient based SEA model is also investigated. In an attempt to validate the numerical work presented in this thesis, experiments have been conducted. Using a wave extraction technique, both the wave amplitudes and plate properties have been evaluated from experimental data, and are subsequently used to experimentally measure the transmission coefficient for two plates coupled at different angles.
16
Chin, Victor B. L. "The dynamic response of pile-soil interfaces during pile driving and dynamic testing events". Monash University, Dept. of Civil Engineering, 2003. http://arrow.monash.edu.au/hdl/1959.1/9421.
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Sen, Sharma Pradeep Kumar. "Stress reduction in a plate with a hole by applied induced strains". Diss., Virginia Tech, 1993. http://hdl.handle.net/10919/27975.
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Jeyanayagam, Samuel S. "Engineering analysis of a Chinese-type anaerobic digester". Diss., Virginia Polytechnic Institute and State University, 1986. http://hdl.handle.net/10919/49800.
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Liu, Xing Lu. "Some problems and analysis for thermal bending plates". Thesis, University of Macau, 2010. http://umaclib3.umac.mo/record=b2148242.
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Chandrashekhara, K. "Geometric and material nonlinear analysis of laminated composite plates and shells". Diss., Virginia Polytechnic Institute and State University, 1985. http://hdl.handle.net/10919/54739.
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An inelastic material model for laminated composite plates and shells is formulated and incorporated into a finite element model that accounts for both geometric nonlinearity and transverse shear stresses. The elasto-plastic material behavior is incorporated using the flow theory of plasticity. In particular, the modified version of Hill's initial yield criterion is used in which anisotropic parameters of plasticity are introduced with isotropic strain hardening. The shear deformation is accounted for using an extension of the Sanders shell theory and the geometric nonlinearity is considered in the sense of the von Karman strains. A doubly curved isoparametric rectangular element is used to model the shell equations. The layered element approach is adopted for the treatment of plastic behavior through the thickness. A wide range of numerical examples is presented for both static and dynamic analysis to demonstrate the validity and efficiency of the present approach. The results for combined nonlinearity are also presented. The results for isotropic results are in good agreement with those available in the literature. The variety of results presented here based on realistic material properties of more commonly used advanced laminated composite plates and shells should serve as references for future investigations.Ph. D.
21
SUBRAMANIAN, BALAKRISHNAN. "GEOMETRICALLY NONLINEAR ANALYSIS OF THIN ARBITRARY SHELLS USING DISCRETE-KIRCHHOFF CURVED TRIANGULAR ELEMENTS (FINITE)". Diss., The University of Arizona, 1985. http://hdl.handle.net/10150/188101.
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The research work presented here deals with the problems of geometrically nonlinear analysis of thin shell structures. The specific objective was to develop geometrically nonlinear formulations, using Discrete-Kirchhoff Curved Triangular (DKCT) thin shell elements. The DKCT elements, formulated in the natural curvilinear coordinates, based on arbitrary deep shell theory and representing explicit rigid body modes, were successfully applied to linear elastic analysis of composite shells in an earlier research work. A detailed discussion on the developments of classical linear and nonlinear shell theories and the Finite Element applications to linear and nonlinear analysis of shells has been presented. The difficulties of developing converging shell elements due to Kirchhoff's hypothesis have been discussed. The importance of formulating shell elements based on deep shell theory has also been pointed out. The development of shell elements based on Discrete-Kirchhoff's theory has been discussed. The development of a simple 3-noded curved triangular thin shell element with 27 degrees-of-freedom in the tangent and normal displacements and their first-order derivatives, formulated in the natural curvilinear coordinates and based on arbitrary deep shell theory, has been described. This DKCT element has been used to develop geometrically nonlinear formulation for the nonlinear analysis of thin shells. A detailed derivation of the geometrically nonlinear (GNL) formulation, using the DKCT element based on the Total Lagrangian approach and the principles of virtual work has been presented. The techniques of solving the nonlinear equilibrium equations, using the incremental methods has been described. This includes the derivation of the Tangent Stiffness matrix. Various Newton-Raphson solution algorithms and the associated convergence criteria have been discussed in detail. Difficulties of tracing the post buckling behavior using these algorithms and hence the necessity of using alternative techniques have been mentioned. A detailed numerical evaluation of the GNL formulation has been carried out by solving a number of standard problems in the linear buckling and GNL analysis. The results compare well with the standard solutions in linear buckling cases and are in general satisfactory for the GNL analysis in the region of large displacements and small rotations. It is concluded that this simple and economical element will be an ideal choice for the expensive nonlinear analysis of shells. However, it is suggested that the element formulation should include large rotations for the element to perform accurately in the region of large rotations.
22
Kumar, Neraj. "Detection of Variable Retention Time in DRAM". PDXScholar, 2014. https://pdxscholar.library.pdx.edu/open_access_etds/2103.
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This thesis investigates a test method to detect the presence of Variable Retention Time (VRT) bits in manufactured DRAM. The VRT bits retention time is modeled as a 2-state random telegraph process that includes miscorrelation between test and use. The VRT defect is particularly sensitive to test and use conditions. A new test method is proposed to screen the VRT bits by simulating the use conditions during manufacturing test. Evaluation of the proposed test method required a bit-level VRT model to be parameterized as a function of temperature and voltage conditions. The complete 2-state VRT bit model combines models for the time-in-state and for the retention-time including miscorrelation. A copula is used to model the eect of miscorrelation between test and use. The proposed VRT test algorithm runtime is estimated as a function of VRT test coverage, test temperature and test voltage.
23
Seward, Lori Welte. "A multiple stress, multiple component stress screening cost model". Thesis, Virginia Tech, 1985. http://hdl.handle.net/10919/41578.
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Environmental stress screening is used to enhance reliability by decreasing the number of failures experienced during customer use. It is suggested that added benefit can be gained by applying multiple stresses rather than a single stress, as is done presently. A further modification is to apply the stress at the assembly level, accelerating different types of components at the same time. Different component E A e acceleration effects must then be considered.
The problem these modifications present is how to choose the appropriate stress levels and the time duration of the stress screen. A cost model is developed that trades off the cost of a field failure with the cost of applying a multiple stress, multiple component stress screen. The objective is to minimize this cost function in order to find an economical stress regimen.
The problem is solved using the software package GINO. The interesting result is that if a stress is used at all during the stress screen, the maximum amount of stress is the economic choice. Either the cost of stressing is low enough to justify the use of a stress, in which case the maximum amount of stress is used, or the cost is too high and the stress is not used at all.
Master of Science
24
Young, David T. "Optimal forms of rectangular-base, shallow shells with respect to buckling". Diss., Virginia Polytechnic Institute and State University, 1985. http://hdl.handle.net/10919/49967.
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Thin, elastic, shallow shells having uniform thickness and rectangular boundaries are investigated. The boundary conditions are either simply supported or claped, and the shell is subjected to a uniformly distributed load applied over either the full shell area or a central region. The thickness, material properties, edge lengths, and surface area of the shell are specified, and the objective is the determination of the shell shape which will maximize the buckling load.
Marguerre's two, coupled, non-linear equations of equilibrium are used to describe prebuckling deformations and stresses. Considering small vibrations about the equilibrium state, two, coupled, linear equations of motion are derived. Subsequently, by recognizing that at buckling the lowest frequency of vibration goes to zero, the buckling equations are obtained. Finally, the Lagrange multiplier technique is employed to formulate an augmented objective function, and the calculus of variations is applied in order to derive the governing set of equations. The resulting system of equations is solved numerically by the finite difference method.
Results for shells with various surface areas are presented. For each surface area the investigation is performed on shells having either clamped or simply supported boundary conditions and either a square or a rectangular boundary. The applied uniform load covers either the full shell area or a partial central region. The shell form, buckling load, and buckling modes of the optimal forms are compared with those of the reference form (double sine) having the same surface area, and changes are noted. Also, comparisons with respect to forms, buckling load, and type of buckling are made between the optimal form of a shell subjected to a full uniform load and the optimal form of the same shell subjected to a partial uniform load.
In some cases, the buckling load of the optimal form is sensitive to imperfections in the form or in the loading distribution as well as to changes in the design. In these cases, some of the apparent advantages of the optimum form may be diminished. Thus, the frequencies of vibration at buckling, the corresponding buckling modes, and the presence of adjacent equilibrium states are monitored in order to evaluate the sensitivity of the optimal form to imperfections and to design changes.Ph. D.
incomplete_metadata
25
Kahle, Matthew Gilbert. "Partially restrained composite connections : design and analysis of a prototype structure". Thesis, Georgia Institute of Technology, 2002. http://hdl.handle.net/1853/20830.
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Heller, Collin M. "A computational model of engineering decision making". Thesis, Georgia Institute of Technology, 2013. http://hdl.handle.net/1853/50272.
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The research objective of this thesis is to formulate and demonstrate a computational framework for modeling the design decisions of engineers. This framework is intended to be descriptive in nature as opposed to prescriptive or normative; the output of the model represents a plausible result of a designer's decision making process. The framework decomposes the decision into three elements: the problem statement, the designer's beliefs about the alternatives, and the designer's preferences. Multi-attribute utility theory is used to capture designer preferences for multiple objectives under uncertainty. Machine-learning techniques are used to store the designer's knowledge and to make Bayesian inferences regarding the attributes of alternatives. These models are integrated into the framework of a Markov decision process to simulate multiple sequential decisions. The overall framework enables the designer's decision problem to be transformed into an optimization problem statement; the simulated designer selects the alternative with the maximum expected utility. Although utility theory is typically viewed as a normative decision framework, the perspective in this research is that the approach can be used in a descriptive context for modeling rational and non-time critical decisions by engineering designers. This approach is intended to enable the formalisms of utility theory to be used to design human subjects experiments involving engineers in design organizations based on pairwise lotteries and other methods for preference elicitation. The results of these experiments would substantiate the selection of parameters in the model to enable it to be used to diagnose potential problems in engineering design projects.
The purpose of the decision-making framework is to enable the development of a design process simulation of an organization involved in the development of a large-scale complex engineered system such as an aircraft or spacecraft. The decision model will allow researchers to determine the broader effects of individual engineering decisions on the aggregate dynamics of the design process and the resulting performance of the designed artifact itself. To illustrate the model's applicability in this context, the framework is demonstrated on three example problems: a one-dimensional decision problem, a multidimensional turbojet design problem, and a variable fidelity analysis problem. Individual utility functions are developed for designers in a requirements-driven design problem and then combined into a multi-attribute utility function. Gaussian process models are used to represent the designer's beliefs about the alternatives, and a custom covariance function is formulated to more accurately represent a designer's uncertainty in beliefs about the design attributes.
27
Stephens, Max Taylor. "Numerical and Experimental Analysis of Composite Sandwich Links for the LCF System". PDXScholar, 2011. https://pdxscholar.library.pdx.edu/open_access_etds/579.
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Shear links are used as fuse elements in lateral load resisting systems to provide ductility and dissipate seismic energy. These links have traditionally been employed in eccentrically braced frames, but have more recently been suggested for use in the innovative linked column frame system (LCF). Current design specifications for shear links require intermediate web stiffeners to provide out-of-plane web stability so ductility requirements can be achieved. This research focused on moving from discrete transverse web stiffening to continuously stiffened webs in built up shear links. Built up links were designed to yield in shear when subjected to severe cyclic loading, however the webs of the links were designed using two metal sheets joined by an elastic core. These composite "sandwich" webs allowed for an increase in web thickness (and inherent flexural rigidity) without increasing the shear strength of the links. Numerical and experimental investigations were conducted to assess the performance of composite sandwich links subjected to severe loading. Numerical results showed improved web behavior in sandwich links in which the core material was assigned an elastic modulus greater than 5000psi. Due to fabrication limitations, experimental specimens were fabricated with a core material elastic modulus of 1000psi. These specimens did not perform as well as unstiffened base case links in terms global hysteretic behavior or ductility.
28
Lokuge, W. P. (Weena Priyanganie) 1967. "Stress-strain behaviour of confined high strength concrete under monotonically increasing and cyclic loadings". Monash University, Dept. of Civil Engineering, 2003. http://arrow.monash.edu.au/hdl/1959.1/9425.
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Perez, Ivan Rodolfo Duran Cruz. "Geração automatica de cenarios de teste a partir de modelos da especificação de sistemas". [s.n.], 2008. http://repositorio.unicamp.br/jspui/handle/REPOSIP/276180.
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Orientador: Eliane MartinsDissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Computação
Made available in DSpace on 2018-08-13T10:23:49Z (GMT). No. of bitstreams: 1 Perez_IvanRodolfoDuranCruz_M.pdf: 1633844 bytes, checksum: e823f99de0cc740109404e263028fac7 (MD5) Previous issue date: 2008
Resumo: As crescentes exigências em relação à melhoria de qualidade e a redução de custos e prazos têm tornado comum à busca por soluções mais eficientes para desenvolvimento e testes de sistemas. Com relação aos testes, uma recomendação é a de começá-los mais cedo, e, de preferência, automatizar o que for possível para evitar enganos cometidos pelos testadores. Assim, uma área de pesquisa que está em evidência atualmente é a de testes baseados em modelos (MBT), onde muitos estudos têm sido realizados visando o desenvolvimento de soluções para automação de testes a partir de modelos criados durante o ciclo de desenvolvimento. Nesta dissertação é proposto um método para geração automática de cenários de teste a partir de modelos da especificação de sistemas, baseando-se em um trabalho prévio para geração de testes de componentes de software. Os modelos utilizados para geração dos testes são os Diagramas de Atividades UML, criados a partir da descrição dos casos de uso, para Testes de Sistemas. A partir deles são gerados cenários de teste que descrevem as interações do sistema, tais como, as ações dos atores e as situações esperadas, incluindo também os cenários de exceção. A aplicação deste método na prática foi feita com êxito por uma equipe de testadores em sistemas reais. De forma geral, os modelos especificados para derivação dos testes têm facilitado o entendimento do sistema pelos testadores envolvidos e as informações presentes nos cenários de teste têm apoiado a realização dos testes.
Abstract: The increasing requirements for quality improvement, reduction of costs and deadlines have promoted the search for more efficient solutions for systems development and testing. In the case of the tests, the recommendation is to start them earlier and, preferably, automatize what is possible to prevent the testers mistakes. Thus, a research area that is in evidence currently is the Model-Based Testing (MBT), in which many studies have been carried out with the aim of development solutions for test automation from the models created during the software development cycle. In this dissertation is proposed a method for automatic generation of test scenarios from the models of systems specification, it is based on a previous work for tests generation of software components. The models used for tests generation are the UML Activities Diagrams, generated from the description of the use cases for System Testing. From them, test scenarios are generated that describe the interactions of the system, such as, the actors actions and the expected situations, including also the exception scenarios. The application of this method in practice was successfully made by a team of testers in real systems. In general, the models specified for tests derivation have facilitated the agreement of the system by the involved testers and, the generated test scenarios contain information that have supported the test execution.
Mestrado
Mestre em Ciência da Computação
30
Bienen, Britta. "Three-dimensional physical and numerical modelling of jack-up structures on sand". University of Western Australia. School of Civil and Resource Engineering, 2007. http://theses.library.uwa.edu.au/adt-WU2007.0208.
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Mobile offshore jack-up drilling rigs are not custom-designed for a particular location but rated for typical operating characteristics, like water depths. They may be deployed at a number of different sites during their design life. Under the current guidelines, the jack-up is required to be assessed for its suitability for each new proposed location, assuming environmental loading conditions due to wind, waves and current corresponding to a 50-year return period storm applicable to the site. Traditionally, these assessments have been performed in two dimensions, simplifying the jack-up to a plane frame and the loading conditions to be in-plane with the rig's 'axis of symmetry'. This thesis introduces a computer program, named SOS_3D, for the fluid-structure-soil interaction analysis of jack-up response in three dimensions. Extensive experimental series have been performed to provide evidence for the generalisation of the foundationsoil interaction model to general six degree-of-freedom loading conditions and its applicability to load paths and stress levels relevant to jack-up spudcans. These experiments included (1) 1g single footing tests, (2) centrifuge single footing tests and (3) centrifuge model jack-up tests. The latter tests highlighted differences in response and mode of failure depending on the loading direction of the jack-up and re-iterated the importance of three-dimensional modelling. The numerical program SOS_3D introduced early in this thesis was shown to represent a useful tool for the prediction of jack-up behaviour under general combined loading in three dimensions. It provided reasonably good, conservative predictions of the experimentally measured jack-up behaviour.
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Widjaja, Budi R. "Analytical investigation of composite diaphragms strength and behavior". Thesis, This resource online, 1993. http://scholar.lib.vt.edu/theses/available/etd-07112009-040307/.
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Mattos, Carlos Eduardo Lourenço. "Metodologia de ensaio de fluência em cabos de transmissão de energia elétrica". Universidade Tecnológica Federal do Paraná, 2015. http://repositorio.utfpr.edu.br/jspui/handle/1/1360.
Texto completo da fonteResumo:
A construção de linhas de transmissão são obras de grande impacto ambiental e requerem grandes investimentos financeiros. Este projeto de pesquisa, visa por meio de ensaios de laboratório, conceber uma ferramenta sistêmica para o aperfeiçoamento do método de determinação da fluência em cabos condutores de energia e OPGW (Optical Ground Wire), que tem sido utilizada no Brasil durante os últimos 30 anos, e analisar os efeitos na construção das linhas aéreas de transmissão. Visa também, proporcionar ganhos de confiabilidade ao sistema de transmissão de energia elétrica, pois o projeto, a construção, a operação e a manutenção de linhas de transmissão dependem de parâmetros de desempenho mecânico dos condutores. Conclui–se que a metodologia de ensaio proposta proporciona resultados finais mais confiáveis quando comparado com o atual procedimento normatizado, utilizado no Brasil, e sua utilização em projetos de linhas aéreas de transmissão de energia podem reduzir custos de construção, aumentar a ampacidade das linhas já existentes, bem como, diminuir os riscos ao a que pessoas estão sujeitas quando expostas a campos elétricos e eletromagnéticos gerados por linhas de transmissão.Overhead Transmission Line construction projects have a great environmental impact and require a large financial investment. This research aims, through laboratory tests, to improve the method of determining the creep of power cables and OPGW (Optical Ground Wire) that has been utilized in Brazil for the last thirty years, as well as analyze the effects on the construction of overhead transmission lines. It will provide greater reliability to the overhead transmission line system, since the design, construction, operation and maintenance of transmission lines depend on the mechanical performance of the conductors. In conclusion, the proposed methodology provides more reliable final results compared to the current standardized procedure and its use in overhead transmission line projects could reduce construction costs, increase the ampacity, as well as reduce the risks to which people are subject when exposed to electric and electromagnetic fields generated by power lines.
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Edouard, Clément. "Vieillissement des batteries Li-ion de traction : des mécanismes vers le vieillissement accéléré". Thesis, Compiègne, 2015. http://www.theses.fr/2015COMP2221/document.
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En raison de leurs performances en termes de densités énergétiques et de puissance, les batteries Li-ion sont les systèmes de stockage électrique privilégiés pour les nouvelles générations de véhicules électriques. Leur modélisation est indispensable pour fournir une évaluation de leurs performances tout au long de leur durée de vie tout en limitant le nombre d'essais expérimentaux, et ceci dans le but de concevoir des configurations et des gestions optimales des packs batteries pour une application envisagée. Le but de ce travail consiste à proposer un modèle physique capable de prédire le comportement et le vieillissement de la batterie sous différentes conditions. Un modèle simplifié électrochimique et thermique capable de prédire le comportement physicochimique et le vieillissement de batteries Li-ion a été étudié. Une analyse de sensibilité a été menée sur l'ensemble des paramètres du modèle dans différentes conditions afin de mettre en évidence leurs influences sur les sorties du modèle. Sur cette base, une méthode d'identification a été proposée pour préserver une indépendance des résultats de l'identification paramétrique par rapport à la sensibilité des paramètres. Cette méthode a permis d'améliorer les prédictions de vieillissement avec des estimations très proches des résultats expérimentaux. Au-delà des gains en compréhension et prédiction, ce modèle physique ouvre de nouvelles possibilités pour établir des protocoles de vieillissement accélérésDue to their high power and energy densities, Li-ion batteries are the leading systems for the new generations of electric vehicles, for which an optimum cell design, management and configuration is essential. Modeling provides tools to perform complex analysis of the performance of Li-ion batteries and reduces the amount of time spent on experimental testing. The aim of our research is to propose a physics-based model that can predict battery behavior and aging under various conditions during the entire lifespan. A simplified electrochemical and thermal model that can predict both physicochemical and aging behaviors of Li-ion batteries has been studied. A sensitivity analysis of all its physical parameters has been performed in order to find out their influence on the model outputs based on simulations under various conditions. The results gave hints on whether a parameter needs particular attention when measured or identified and on the conditions under which it is the most sensitive. A specific simulation profile has been designed for parameters involved in aging equations in order to determine their sensitivity. Finally, a step-wise method has been followed to limit the influence of parameter values when identifying sorne of them. This sensitivity analysis and the subsequent step-wise identification method show very good results, such as a better fitting of the experimental data with simulated cell voltage. Beyond advanced comprehension and prediction, this physical model opens new possibilities to define accelerated aging tests
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Thölken, Denise. "Efeito da rigidez de pilar parede no comportamento sísmico de edifício de concreto armado". Universidade Tecnológica Federal do Paraná, 2013. http://repositorio.utfpr.edu.br/jspui/handle/1/962.
Texto completo da fonteResumo:
Este trabalho tem como objeto o estudo do efeito da rigidez de pilar parede no comportamento estrutural de edifícios de concreto armado submetidos a sismos. Foram consideradas as premissas da norma brasileira ABNT NBR15421:2006, que apresenta os critérios para projeto de estruturas resistentes a sismo. A análise linear com emprego dos métodos da norma - método das forças horizontais equivalentes, método espectral e histórico de aceleração no tempo - foi aplicada em edifícios com dois tipos de sistemas estruturais, sendo eles pórtico de concreto e sistema dual pórtico de concreto e pilar parede. Os resultados foram analisados nos pórticos de extremidade das estruturas nos sentidos longitudinal (x) e transversal (y), comparando-se os deslocamentos de cada pavimento e esforços cortantes, momento fletor e normal nas bases dos pilares. A comparação foi realizada entre os três métodos aplicados e os sistemas estruturais analisados.The aim of this work is to study the stiffness effect of wall columns on structural behavior of reinforced concrete buildings subjected to seismic action. The premises of the Brazilian standard ABNT NBR14521:2006 were considered, which presents criteria for earthquake resistant design of structures. The linear analysis employed the methods of the Brazilian standard - equivalent static load method, response spectrum analysis and time history method - were applied to buildings with two types of structural systems, namely concrete frame and dual system concrete frame and wall columns. The results were analyzed in edge frames structures in the longitudinal and transverse directions, comparing the displacement of each floor and shear, bending moment and axial forces on the bases of the columns. A comparison was made between the three methods applied and the structural systems analyzed.
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Pessôa, José Renato de Castro. "Análise numérico-experimental de estruturas de concreto com utilização da energia de fraturamento". Universidade do Estado do Rio de Janeiro, 2007. http://www.bdtd.uerj.br/tde_busca/arquivo.php?codArquivo=780.
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Coordenação de Aperfeiçoamento de Pessoal de Nível SuperiorA evolução dos concretos utilizados nas últimas décadas deu origem ao Concreto de Alto Desempenho (CAD), que tem, entre suas características, alta resistência à compressão e baixa permeabilidade. Com o desenvolvimento dos produtos químicos utilizados na construção civil, em especial os superplastificantes e superfluidificantes, a utilização desse tipo de concreto tornou-se cada vez mais freqüente pela possibilidade de se obter uma mistura suficientemente trabalhável utilizando-se fatores água/cimento menores do que 0,35. Devido à sua microestrutura mais homogênea, esse tipo de concreto apresenta um comportamento mais frágil do que os concretos convencionais, exigindo uma melhor caracterização do material. A partir do final da década de 70 começou-se a aplicar os conceitos da Mecânica da Fratura para análise do comportamento de estruturas construídas com esse tipo de concreto. Como em algumas situações a resistência nominal de peças de concreto diminui com o aumento de suas dimensões, houve a necessidade de se considerar o efeito de escala das estruturas a fim de se obter níveis de segurança mais adequados no seu dimensionamento, o que justificou a utilização da Mecânica da Fratura. Neste trabalho a energia de fraturamento foi obtida experimentalmente pelo método do trabalho de fraturamento e pelo método do efeito de escala, por meio de ensaios estáveis de flexão de três pontos em amostras de concreto de alto desempenho com entalhe. Foi também desenvolvida a simulação numérica de uma viga com entalhe, analisada pelo método dos elementos finitos e empregando-se na modelagem constitutiva os conceitos da Mecânica da Fratura aplicada ao concreto. As vigas foram moldadas e ensaiadas no Instituto Politécnico do Rio de Janeiro (IPRJ) da Universidade do Estado do Rio de Janeiro (UERJ) na cidade de Nova Friburgo. Os ensaios foram realizados com controle de deslocamento da célula de carga. Foram ensaiadas três séries de 12 vigas, com quatro dimensões diferentes, geometricamente proporcionais, e três amostras para cada dimensão, totalizando 36 vigas. As alturas utilizadas para as vigas foram 38, 76, 152 e 304 mm, e sua espessura foi mantida constante igual a 38 mm. Os corpos de prova cilíndricos, para caracterização da resistência à compressão do concreto, foram moldados no IPRJ e rompidos no laboratório de engenharia civil da UERJ, na cidade do Rio de Janeiro. Os concretos utilizados apresentaram resistência à compressão média de 70 MPa.
The evolution of the concrete mixes used during the last decades gave birth to the High Performance Concrete (HPC), which, among its main characteristics, presents high strength and low permeability. With the development of chemical products used in civil engineering constructions, mainly the superplasticizers, the use of this kind of concrete has become more and more frequent due to the possibility of obtaining a workable mixture with a water/cement ratio lower than 0.35. Due to its more homogeneous microstructure, the HPC presents a more fragile behavior than the conventional concrete, demanding a better characterization of the material. At the end of the 1970s, concepts of the Fracture Mechanics started to be used for the analysis of the structural behavior of concrete structures. As the nominal stress of the material decreases as the size of the structure increases, it became necessary to consider this size effect in the analysis in order to obtain more suitable levels of security. This fact justifies the use of the Fracture Mechanics in the structural analysis of concrete structures. In this work, the fracture energy was experimentally obtained using the work-offracture method and the size effect method by performing three-point bend tests in HPC notched beams. It was also developed a numerical simulation of the tests, performing the analysis through the Finite Element Method and applying the concepts of the Fracture Mechanics of Concrete into the constitutive model. The notched beams were molded and tested at the Polytechnic Institute of the State University of Rio de Janeiro (IPRJ/UERJ), located in the city of Nova Friburgo. The tests were controlled by the vertical displacement of the load cell. Three series of twelve beams with four geometrically similar sizes were tested. Three samples for each size were cast, making an amount of 36 beams. The beams were 38, 76, 152 and 304 millimeters high and the width was kept constant equal to 38 millimeters. To characterize the concrete compression strength, 100x200 millimeters cylinders were molded at the IPRJ and tested at the UERJ civil engineering laboratory in the city of Rio de Janeiro. The tested concretes presented a medium compressive strength of 70 MPa.
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Nahan, Matthew F. "A nonlocal damage theory for laminated plate with application to aircraft damage tolerance". Thesis, 1997. http://hdl.handle.net/1957/34015.
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Design of commercial aircraft structure, composed of composite material, requires the
prediction of failure loads given large scale damage. In particular, a fuselage of
graphite/epoxy lamination was analyzed for damage tolerance given a standard large
crack that severed both skin and internal structure. Upon loading, a zone of damage is
known to develop in front of a crack-tip in composite laminates; and, its material
behavior within the damage zone is characterized as strain softening. This investigation
sought to develop a computational model that simulates progressive damage growth and
predicts failure of complex laminated shell structures subject to combined tensile and
flexural load conditions. This was accomplished by assuming a macroscopic definition
of orthotropic damage that is allowed to vary linearly through the shell thickness. It was
further proposed that nonlocal plate strain and curvature act to force damage growth
according to a set of uniaxial criteria. Damage induced strain softening is exhibited by
degradation of laminate stiffness. An expression for the damage reduced laminated
plate stiffness was derived which assumed the familiar laminated plate [AM] stiffness
matrix format. The model was implemented in a finite element shell program for
simulation of fracture and evaluation of damage tolerance. Laminates were characterized
for damage resistance according to material parameters defining nonlocal strain and
the damage growth criteria. These parameters were selected using an inverse method to
correlate simulation with uniaxial strength and fracture test results. A novel combined
tension-plus-flexure fracture test was developed to facilitate this effort. Analysis was
performed on a section of pressurized composite fuselage containing a large crack.
Good agreement was found between calculations and test results.Graduation date: 1998
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Wu, Y. F. (Yu-Fei). "Seismic retrofitting of rectangular reinforced concrete columns with partial interaction plating". 2002. http://web4.library.adelaide.edu.au/theses/09PH/09phw9591.pdf.
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Wu, Y. F. (Yu-Fei). "Seismic retrofitting of rectangular reinforced concrete columns with partial interaction plating / by Yu-Fei Wu". Thesis, 2002. http://hdl.handle.net/2440/21836.
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"June 2002"Includes bibliographical references (leaves 349-374)
xxxix, 416 leaves : ill., plates ; 30 cm.
Thesis (Ph.D.)--University of Adelaide, Dept. of Civil and Environmental Engineering, 2002
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Young, Andrew J. "Active control of vibration in stiffened structures". Thesis, 1995. http://hdl.handle.net/2440/37722.
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Active control of vibration in structures has been investigated by an increasing number of
researchers in recent years. There has been a great deal of theoretical work and some
experiment examining the use of point forces for vibration control, and more recently, the use
of thin piezoelectric crystals laminated to the surfaces of structures. However, control by
point forces is impractical, requiring large reaction masses, and the forces generated by
laminated piezoelectric crystals are not sufficient to control vibration in large and heavy
structures.
The control of flexural vibrations in stiffened structures using piezoceramic stack actuators
placed between stiffener flanges and the structure is examined theoretically and
experimentally in this thesis. Used in this way, piezoceramic actuators are capable of
developing much higher forces than laminated piezoelectric crystals, and no reaction mass is
required. This thesis aims to show the feasibility of active vibration control using
piezoceramic actuators and angle stiffeners in a variety of fundamental structures.
The work is divided into three parts. In the first, the simple case of a single actuator used to
control vibration in a beam is examined. In the second, vibration in stiffened plates is
controlled using multiple actuators, and in the third, the control of vibration in a ring-stiffened
cylinder is investigated.
In each section, the classical equations of motion are used to develop theoretical models
describing the vibration of the structures with and without active vibration control. The
effects of the angle stiffener(s) are included in the analysis. The models are used to establish
the quantitative effects of variation in frequency, the location of control source(s) and the
location of the error sensor(s) on the achievable attenuation and the control forces required
for optimal control. Comparison is also made between the results for the cases with multiple
control sources driven by the same signal and with multiple independently driven control
sources. Both finite and semi-finite structures are examined to enable comparison between
the results for travelling waves and standing waves in each of the three structure types.
This thesis attempts to provide physical explanations for all the observed variations in
achievable attenuation and control force(s) with varied frequency, control source location and
error sensor location. The analysis of the simpler cases aids in interpreting the results for the
more complicated cases.
Experimental results are given to demonstrate the accuracy of the theoretical models in each
section. Trials are performed on a stiffened beam with a single control source and a single
error sensor, a stiffened plate with three control sources and a line of error sensors and a ring-stiffened
cylinder with six control sources and a ring of error sensors. The experimental
results are compared with theory for each structure for the two cases with and without active
vibration control.Thesis (Ph.D.) -- University of Adelaide, Dept. of Mechanical Engineering, 1995.
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"Statistical learning and testing approaches for temporal dependence structures with application to financial engineering". Thesis, 2003. http://library.cuhk.edu.hk/record=b6073941.
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A technique called gaussian temporal factor analysis (gaussian TFA) proposed by Xu in 2000 may be used to test the APT model under the mild assumption that the efficient market hypothesis (EMH) is violated. We are motivated to investigate statistical behaviors of the gaussian TFA model.According to a recent survey by Cochrane (1999), the multi-factor APT model is gaining popularity and recognition over CAPM by the investment community. While empirical evidence shows that mutual funds can earn average returns not explained by the CAPM by following a variety of investment styles, this anomaly could be captured by APT which includes the single-factor CAPM as a special case. Yet, three aspects of APT still cannot be tested in practice.
First, a systematic testing package is proposed for testing gaussian TFA in six dimensions, including factor number, factor loadings, residuals correlations and autoregressive conditional heteroscedasticity (ARCH) effects, economic significance and factor independence, using financial data in Hong Kong. Particularly, a new hypothesis testing approach is proposed for statistically testing independence.
In the finance literature, an objective way to judge whether an asset pricing model is misspecified is by statistical tests. In the past, both the capital asset pricing model (CAPM) and the arbitrage pricing theory (APT) have been the subjects of extensive tests.
Second, we investigate two extensions of the gaussian TFA model in view of ARCH in driving noise residuals. We test the extended models for ARCH as well as other aspects to ensure model specification adequacy. Furthermore, we find that ARCH effects are not quite significant driving noise residuals of the macroeconomic modulate independent state-space model. This may be due to long-term modelling of the market.
Third, we test gaussian TFA from the practical point of view in financial prediction and portfolio management. For prediction, we introduce the gaussian TFA alternative mixture experts (ME) approach for forecasting. For adaptive portfolio management, we derive the gaussian TFA adaptive algorithm for implementing the Sharpe-ratio based adaptive portfolio management under different scenarios. Empirical results reveal that APT-based portfolio management techniques are in general superior to return-based techniques.
by Kai-Chun Chiu.
"July, 2003."
Adviser: Lei Xu.
Source: Dissertation Abstracts International, Volume: 64-09, Section: B, page: 4451.
Thesis (Ph.D.)--Chinese University of Hong Kong, 2003.
Includes bibliographical references (p. 113-125).
Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web.
Electronic reproduction. Ann Arbor, MI : ProQuest dissertations and theses, [200-] System requirements: Adobe Acrobat Reader. Available via World Wide Web.
Electronic reproduction. Ann Arbor, MI : ProQuest Information and Learning Company, [200-] System requirements: Adobe Acrobat Reader. Available via World Wide Web.
School code: 1307.
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Schumann, Erwin Wilhelm. "Modelling and testing microwave magnetrons". Thesis, 1988. http://hdl.handle.net/10413/6903.
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Though declining in popularity over the last decade, the magnetron
still has applications where portable high power is needed. This study
examines the predicted performance of cylindrical microwave magnetrons
using analytic lumped-spoke models based on the energy conservation
principle. The analytic approach is still favoured when small computer
systems are used and the overall performance of the tube is to be
predicted. The magnetron elements are examined and the role they play
in the overall device performance analysed. Simplified representations
of these elements are used to construct a complete magnetron model.
The Hartree threshold condition is reexamined and a new, more accurate
analytic formulation proposed. This formulation is based on electric
field strengths at the base of the magnetron spoke. The effect of the
space charge on the threshold condition is included. Spoke current has
been evaluated at the edge of the Brillouin hub. The resulting anode- cathode
voltage performance predictions are consistent with measured
results. A computer program has been written to analyse the
performance predicted by this model. Models proposed by other authors
are examined, and compared to this model. The resulting model has been
tested by comparing predicted results to the measured performance of
four slot-and-hole magnetrons.
To facilitate accurate magnetron testing, a new automated triple-stub
high power microwave load has been developed. The load operates at a
peak power of IMW from 2,7-3,OGHZ, and allows the change of the VSWR
to any value along any path within the VSWR=I, 5: I circle. The
development of the triple tuner and termination is discussed in
detail. A new waterload configuration which has the advantage of
simple construction yet good matching characteristics is presented.
Automated measurement of pulling figure and construction of Rieke
diagrams is discussed. The accuracy of the complete load is compared
to conventional loads currently in service in the tube industry.Thesis (Ph.D.)-University of Natal, Durban, 1988.
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Meyers, Anthony G. (Anthony Gerard). "The determination of rock mass strength for engineering design / Anthony G. Meyers". 1993. http://hdl.handle.net/2440/20601.
Texto completo da fonteResumo:
Bibliography: leaves 385-395xxv, 395 leaves : ill ; 30 cm.
Title page, contents and abstract only. The complete thesis in print form is available from the University Library.
Thesis (Ph.D.)--University of Adelaide, Dept. of Civil Engineering, 1993
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Meyers, Anthony G. (Anthony Gerard). "The determination of rock mass strength for engineering design / Anthony G. Meyers". Thesis, 1993. http://hdl.handle.net/2440/20601.
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Tso, Y. (Yan). "A study of the transmission of vibration in structures characteristic of naval ships / Yan Tso". 1996. http://hdl.handle.net/2440/18755.
Texto completo da fonteResumo:
Bibliography: leaves 159-169.xii, 170 leaves : ill. (some col.) ; 30 cm.
Title page, contents and abstract only. The complete thesis in print form is available from the University Library.
This thesis is concerned with the transmission and distribution of vibratory power in built-up structures, and in particular, structures characteristic of naval ships. The study consists of a detailed investigation of the wave transmission properties of structural junctions, followed by an analysis of the wave propagation through plates with periodic stiffeners. The results are used to develop Statistical Energy Analysis (SEA) models for the prediction of vibration levels in structures characteristic of naval ships.
Thesis (Ph.D.)--University of Adelaide, Dept. of Mechanical Engineering, 1996
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Tso, Y. (Yan). "A study of the transmission of vibration in structures characteristic of naval ships / Yan Tso". Thesis, 1996. http://hdl.handle.net/2440/18755.
Texto completo da fonteResumo:
Bibliography: leaves 159-169.xii, 170 leaves : ill. (some col.) ; 30 cm.
This thesis is concerned with the transmission and distribution of vibratory power in built-up structures, and in particular, structures characteristic of naval ships. The study consists of a detailed investigation of the wave transmission properties of structural junctions, followed by an analysis of the wave propagation through plates with periodic stiffeners. The results are used to develop Statistical Energy Analysis (SEA) models for the prediction of vibration levels in structures characteristic of naval ships.
Thesis (Ph.D.)--University of Adelaide, Dept. of Mechanical Engineering, 1996
46
Liang, Bin. "Estimation of Time-dependent Reliability of Suspension Bridge Cables". Thesis, 2016. https://doi.org/10.7916/D8V69JTN.
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The reliability of the main cable of a suspension bridge is crucial to the reliability of the entire bridge. Throughout the life of a suspension bridge, its main cables are subject to corrosion due to various factors, and the deterioration of strength is a slowly evolving and dynamic process. The goal of this research is to find the pattern of how the strength of steel wires inside a suspension bridge cable changes with time. Two methodologies are proposed based on the analysis of five data sets which were collected by testing pristine wires, artificially corroded wires, and wires taken from three suspension bridges: Severn Bridge, Forth Road Bridge and Williamsburg Bridge.
The first methodology is to model wire strength as a random process in space whose marginal probability distribution and power spectral density evolve with time. Both the marginal distribution and the power spectral density are parameterized with time-dependent parameters. This enables the use of Monte Carlo methods to estimate the failure probability of wires at any given time. An often encountered problem -- the incompatibility between the non-Gaussian marginal probability distribution and prescribed power spectral density -- which arises when simulating non-Gaussian random processes using translational field theory, is also studied. It is shown by copula theory that the selected marginal distribution imposes restrictions on the selection of power spectral density function.
The second methodology is to model the deterioration rate of wire strength as a stochastic process in time, under Ito's stochastic calculus framework. The deterioration rate process is identified as a mean-reversion stochastic process taking non-negative values. It is proposed that the actual deterioration of wire strength depends on the deterioration rate, and may also depend on the state of the wire strength itself. The probability distribution of wire strength at any given time can be obtained by integrating the deterioration rate process. The model parameters are calibrated from the available data sets by matching moments or minimizing differences between probability distributions.
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Karanci, Efe. "Modeling Corrosion in Suspension Bridge Main Cables". Thesis, 2017. https://doi.org/10.7916/D8RB7H05.
Texto completo da fonteResumo:
Accurately determining the current state of a suspension bridge’s main cables is a critical component to reliably assessing the safety of the bridge. The primary cause for the deterioration of cable strength with time is universally recognized to be the corrosion of high strength steel wires, which together comprise the main cable. Hidden from view by the cable wrapping, this corrosion often goes undetected for years and is typically only discovered during costly and intrusive inspections. Furthermore, current inspection methods provide an incomplete picture of the variation in wire condition across the cable cross section. As a result, cable strength estimation techniques that rely solely on inspection data introduce a considerable degree of uncertainty. Finally, a method has not been developed for estimating the continuing decline in cable strength due to ongoing corrosion. A recent direction in research attempts to address the shortcomings of current inspection methodologies and the intent of this thesis is to further build upon these findings.
In these recent studies, environmental conditions inside main cables are monitored to obtain information regarding the corrosive nature of the cable’s internal environment. The first goal of this thesis is to further this research direction by introducing a corrosion rate model for bridge wires that relates the monitored environmental parameters within a cable to the corrosion rate of bridge wires. Initially, temperature, relative humidity, pH, and Cl- concentration have been identified as the most relevant variables for predicting the corrosion rate of a bridge wire. By applying machine learning methods to a corrosion dataset in conjunction with these monitored environmental inputs, a long term corrosion rate model for bridge wires has been developed that is capable of capturing variability associated with these environmental parameters.
This long term corrosion rate model is then applied to establish a methodology that will allow bridge owners and engineers to estimate the remaining strength of a main cable at any point in time. This is accomplished through the use of continually monitored environmental parameters which are input into the corrosion rate model. Incorporating the long term corrosion rate model developed in this thesis with current strength estimation techniques, the methodology presented in this thesis for the estimation of the remaining strength of suspension bridge cables may be readily adapted to other bridges and can be used to complement the current best practices for bridge inspection.
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Law, J. R. "Time varying probability of failure of steel floor beams subjected to real fire". Thesis, 1997. https://vuir.vu.edu.au/18185/.
Texto completo da fonteResumo:
A model for estimating the time-dependent reliability of steel beams under real fire
conditions has been developed. It gives a more rational basis than time of failure
modelling does for design. From risk modelling, some small resistance time from the
probabilistic distribution times of failure can be deduced, which gives an acceptably
small risk of failure. Time of failure modelling by itself can only give the mean time failure which could lead to excessive risk if the variability of time of failure is large. The model comprises submodels for fire severity, heat transfer, mechanical properties, loads,
structural analysis and reliability. Simple submodels have been adopted commensurate
with the level of accuracy of other models in fire safety engineering. The submodel for
real fire severity is Lie's. Heat transfer submodels have been adopted for three and four
sided exposure and have been taken from work by the European Regional Organisation
for Steel Construction and the French Technical Centre for Steel Construction. Three
sided arises when the beam supports a concrete slab. The mechanical properties
submodel was derived from an empirical fit to available test data. It gave better results
than the current model in AS4100. It is appropriate for the model but is too complex for
replacing the model in AS4100. The structural model four sided exposure was
developed from simple plastic theory. For three sided exposure, discrete element
analysis was adopted. The load submodels were lognormal for dead load and Weibull
arbitrary point in time values for live load. The Monte Carlo method was adopted for the
reliability submodel. The overall model was used to obtain the following sensitivities.
An increase of lOkg.m-2 in fire load density can increase the risk of failure by 40%. In
relation to the sensitivity of risk to ventilation, a reduction of the opening factor from
0.12 to 0.04 m0.5 increases the risk of failure approximately 200 times. Doubling the
insulation thickness reduces the risk of failure by a factor ten. Increasing the live load
has less effect on the risk of failure than increasing the dead load. If the load present predominantly live load, there is much less risk of failure than if the load is
predominantly live load. Four sided exposure has ten times the risk of failure compared
with three sided exposure. Accepting larger proof strains reduces the risk of failure; for
example, increasing proof strain from 0.2% to 1% reduces the risk of failure by 50%.
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Knoesen, Darryn Marc. "The development and assessment of techniques for daily rainfall disaggregation in South Africa". Thesis, 2005. http://hdl.handle.net/10413/3439.
Texto completo da fonteResumo:
The temporal distribution of rainfall , viz. the distribution of rainfall intensity during a storm, is an important factor affecting the timing and magnitude of peak flow from a catchment and hence the flood-generating potential of rainfall events. It is also one of the primary inputs into hydrological models used for hydraulic design purposes. The use of short duration rainfall data inherently accounts for the temporal distribution of rainfall, however, there is a relative paucity of short duration data when compared to the more abundantly available daily data. One method of overcoming this is to disaggregate courser-scale data to a finer resolution, e.g. daily to hourly. A daily to hourly rainfall disaggregation model developed by Boughton (2000b) in Australia has been modified and applied in South Africa. The primary part of the model is the . distribution of R, which is the fraction of the daily total that occurs in the hour of maximum rainfall. A random number is used to sample from the distribution of R at the site of interest. The sample value of R determines the other 23 values, which then undergo a clustering procedure. This clustered sequence is then arranged into 1 of 24 possible temporal arrangements, depending when the hour the maximum rainfall occurs. The structure of the model allows for the production of 480 different temporal distributions with variation between uniform and non-uniform rainfall. The model was then regionalised to allow for application at sites where daily rainfall data, but no short duration data, were available. The model was evaluated at 15 different locations in differing climatic regions in South Africa. At each location, observed hourly rainfall data were aggregated to yield 24-hour values and these were then disaggregated using the methodology. Results show that the model is able to retain the daily total and most of the characteristics of the hourly rainfall at the site, for when both at-site and regional information are used. The model, however, is less capable of simulating statistics related to the sequencing of hourly rainfalls, e.g. autocorrelations. The model also tends to over-estimate design rainfalls, particularly for the shorter durations .Thesis (M.Sc.)-University of KwaZulu-Natal, Pietermaritzburg, 2005.
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Beale, Michael P. "New Approaches to Analyze Sound Barrier Effectiveness". 2012. http://hdl.handle.net/1805/3240.
Texto completo da fonteResumo:
Indiana University-Purdue University Indianapolis (IUPUI)Highway noise can cause annoyance, affect sleep patterns, and reduce the property value for people in the proximity. Current methods for analyzing the effectiveness of sound barriers only take loudness into consideration. This paper introduces new methods that can be used to analyze the effectiveness of the sound barriers. Our approach uses psychoacoustic measures including sharpness, roughness, fluctuation, strength, and annoyance. Highway noise is non-stationary, therefore each of these metrics are calculated over a short time. Finally analysis is performed the distribution and change over time. We used nth nearest neighbor algorithm to remove sounds that are not a part of the experiment. In the future, this data can be combined with human surveys to see if the change in sound quality due to the presence of sound barriers has a meaningful impact on people's lives.